VEHICLES ploughed through pedestrians in two Sydney suburbs yesterday, injuring eight people.

In the morning, customers at a car wash at Smithfield had a narrow escape with only minor injuries after the driver of a semitrailer lost control and ran into six cars.

Pedestrians outside a Penrith real estate agent were less fortunate a few hours later when a car which police said was driven by an elderly woman ploughed through them and into a shopfront, narrowly missing a baby.

Six people were taken to Nepean Hospital, two with serious head injuries, an ambulance spokesman said.

The car, believed to be a Hyundai, ran into the front of Michael Ball Realty.

Lisa Hall, who owns Boutique Hair Design next door, said among the pedestrians hit was a man carrying a baby. "He got pinned to the side of the real estate [agency]," she said.

Ms Hall said he had been walking with two elderly people, believed to be the child's grandparents, who had been pushing a pram. But it was empty when the car hit, she said.

"The pram went flying at the time and I was just trying to find this baby. If that baby was in the pram … " She said the two elderly people suffered serious head injuries.

Michael Ball, whose shop was hit, said he was walking into the premises when he heard a bang, which he believed was the Hyundai hitting a parked car on Woodriff Street. "I turned around to see what it was and saw this car flying towards the window."

He said it smashed a bus stop bench before hitting four people and pinning a man to the front of his agency.

"The man had been stuck between the car and the window and he was still holding the baby in his arms," he said. "The baby was fine, a little champion. I was more surprised the man was able to hold on to the baby - he's an absolute legend."

The earlier accident occurred when a truck travelling down the Cumberland Highway at Smithfield went out of control and hit a light pole, before ploughing into Jimmy's Car Wash about 9.30am.

Two people were injured in the accident. The truck driver was unhurt. Ron Phillips, an attendant at a service station across the road, said: "It looks like the truck hit a pole and then jumped the island. I can see at least six cars that he's wiped out."